Variable frequency oscillation generator



Dec. 6, 1949 J. D. wooDwARD VARIABLE FREQUENCY QSCILLATION GENERATOR 4 Sheets-Sheet l Filed April 23. 1947 Ummm rv m Nrolb INVENTOR. (/025/1 Wodzzzm/ ATTORNEY.

'Dem 6; v1949 I D. WOODWARD l 2,490,499

VARIABLE FREQUENCY OSCILLATION GENERATOR Filed April 2 5, 1947 y 4 Sheets-Sheet 2 INVENTOR.

ATTORNEY.

De- 6, 1949 l J. D. WOODWARD 2,490,499

VARIABLE FREQUENCY OSCILLATION GENERTOR Filed April 25, 1947 4 Sheets-Sheet 3 -2/ V01. rs

INVENTOR.

c/n LZ). WMe/wald Dec. 6, 1949 J. n. wooDwARD VARIABLE FREQUENCY OSCILLATION GENERATOR 4 Sheets-Sheet' 4 Filed April 23, 1947 INVENTOR. c/azz Woa/zanz ATTORNEY.

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Patented Dec. 6, 1 949 VARIABLE FREQUENCY OSCILLATION GENERATOR John D. Woodward, Sewell, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application April 23, 1947, Serial No. 743,234

(Cl. Z50- 236) 8 Claims.

This invention relates to variable frequency oscillation generators and has for its principal object the provision of an improved apparatus and method of operation whereby the output frequency of such a generator may be varied over a considerable range -by equal steps and may be stabilized with crystal accuracy at each of these steps.

For accomplishing this result, there is provided an oscillation generator having control means whereby its output frequency may be varied by substantially equal steps over the desired frequency range. The output of this generaf tor is supplied to a counter or frequency divider which is so controlled in conjunction with the generator as to produce a substantially constant low frequency. This substantially constant low frequency is applied to a phase detector. Also applied to this phase detector is a constant frequency derived from a crystal controlled generator through a counter or frequency divider havinga fixed division ratio, or derived from some other standard frequency source such as a tuning fork. The output of the' phase detector is utilized to control the reactance of a reactance tube by which the frequency of the variable frequency generator is held to crystal accuracy at each stepv of itsadjustment.

. So long as the substantially constant low frequency derived from the adjustable counter is at its proper value, the phase relation between this frequency and that derived from the constant frequency source is constant andthe effect of the reactance tube on the frequency of the variable frequency generator is constant. When the frequency derived from tthe adjustable counter tends to change, however, there is applied from the phase detector to the reactance tube a control potential by which the output frequency of the variable frequency generator is restored to its proper value. This of course restores the proper phase relation between the two low frequencies applied to the phase detector so that, at' 'any one of its selected output frequencies, the variable frequency lgenerator operates with crystal-controlled accuracy.

T Considered from another viewpoint, the ganged controls of the variable frequency generator and the adjustable cycle counter function as a coarse frequency regulating means and the constant frequency source together with its fixed division ratio counter function as a ne frequency regulating or stabilizing means.

Important objects of theinvention are the provision of an improved variable frequency gerera 2 tor which is adapted to have its output frequency adjustedby equal stepspand accurately stabilized at each of these steps; and the provision of a variable frequency generator which is free running over a predetermined frequency range vto produce, with crystal controlled accuracy, frequencies separated in value by predetermined submultiples of such range.

The invention will be better understood from the following description considered in connection with the accompanying drawings and its scope is indicated by the appended claims.

Referring to the drawings:

Fig. 1 is a block. diagram indicating the relation between the various parts of the apparatus,

Fig. 2 is a wiring diagram showing the connections of the constant frequency generator, the fixed division ratio counter, the phase detector.' the reactance tube, the variable frequency generator and a frequency divider which connectsv the variable frequency generator to the` adjust-j able cycle counter,

Fig. 3 isa wiring diagram-of the adjustable cycle counter, and Figs. 4 to '7 are explanatory diagrams relating. tothe operation of the adjustable cycle counter.- Fig.. lv shows a constant frequency source 241Vr from which oscillations are supplied through a frequency divider 248 and a lead 249 to a phasedetector 250. oscillations of substantially con. stant frequency are also supplied to the phase detector 25E from an adjustable4 cycle counter 25,4through a lead 62. The output of the phase detector 250 `is supplied to a controllable or variable frequency generator 252 through a lead 25.1. The outp'ut of the generator 252 is supplied through. a lead 204 to .a fixed division ratio counter'.v or frequency divider 253.which is con--l nected througha Iead 255 to the adjustable cyclef counter254. The counter 254 is provided with a units control switch 8l, a tens control switch 941,.a hundreds control switch 95 and a thousands control switch 96. By manipulation of these .control switches, output pulses, of substantially constant frequency may be produced at the lead 6,2 in response to Variable frequency pulses delivered through the lead A255. A s here-- inafter explained'in connection with Fig. 3, the; switches 95. and 96 may be ganged together so that thefre'quency division ratio of the counter is va'ri'able'over a range of 1400 to 2399 input pulses and a single output pulse is applied to the lead $2 in response'to any number of input pulses within this range. l The variable frequencyA generator is provided with four control switches. Three of these switches, 242, 243 and 244 function to connect different tuning coils into the tank circuit of the generator for producing equal and relatively large steps in the generator output frequency. The fourth switch 245 functions to connect to the selected tuning coil a plurality of inductance units which are varied in value to produce an equal number of relatively small steps over the range of each of the relatively large steps. In this way, the output frequency of the generator 252 is varied by equal and relatively small steps over a predetermined range.

For purpose of illustration it is assumed that (1) the constant frequency generator 241 delivers a frequency of 100 k. c. which is reduced by the frequency divider 248 to a frequency of 62.5 cycles so that this frequency is applied through the lead 249 to the phase detector 256, (2) the control switch 242, 243 and 244 are so connected that the output frequency of the generator 252 is 700 k. c. when they are in their number 1 positions and is increased by 50 k. c. steps as these switches are moved clockwise into engagement with the successive fixed contacts, and (3) the movement of the switch 245 into engagement withitssuccessive fixed contacts divides each 50 k. c. step into ten 5 k. c. steps. This means that the output frequency of the generator 252 is varied over a range of 700 k. c. to 1195 k. c. by equal steps of 5 k. c. Thus the cycle of operation is movement of the switches 242, 243 and 244 from one xed -contact to another, movement of the switch 245 over all its fixed contacts and subsequent repetition of these two operations.

As hereinafter explained in connection with Fig.2, the division ratio of the frequency divider 253 is 16 so that lthe input frequency of the cycle counter 254 varies over a range of 74,687.5 to 43,750 cycles. If the substantially constant output frequency at the lead 62 is to be 31.25 cycles, this means that the division ratio of the counter 254 must be variable over a range of 2399 to 1400. Thus for the 700 k. c. output of the generator 252, the various control switches of Fig. 1 are set to their illustrated positions as a result of which the 700 k. c. tuning coil is connected in the generator tank circuit in series with the maximum number of inductance units and the counter 254 is set for a division ratio of 1400. Under these conditions, pulses are delivered at the output lead 62 at a frequency of 31.25 cycles per second.

From this '700 k. c. value. the generator output frequency is increased to 745 k. c. by 5 k. c. steps in response to movement of the switch 245 and at the same time the switch 94 is rotated to increase the division ratio of the counter 254 by stens of ten. From 745 k. c., the generator output freouencv is increased to'750 k. c. by moving the switches 242. 243 and 244 to their 2 positions and the switch 95 to its 5 position. From its 750 k. c. value. the generator output frequency is increased by 5 k. c. steps to 795k. c. by operation of the switch 245 and at the same time the division ratio isincreased by steps of as described above. Further increases in the generator frequency are effected by following thefsame procedure with the other tuning coils ofthe generator.

The constant frequency generator 241 is illustr-ated in Fig. 2 as of a conventional crystal controlled type. The frequency divider 248 is shown as including a plurality of stages 256 to 261. The four high speed stages 256 to 259 are interconnected in. a well known manner to form a decade counter which delivers, at the lead 268. one output pulse for every ten pulses applied to the input lead 269 from the generator 241. The intermediate speed stages 26D to 262 are connected in tendem so that they deliver one output pulse at the lead 210 for every eight pulses applied to the input lead 269. The next four stages 263 to 266 are connected to function as a decade counter so that they deliver one pulse at their output lead 21| for each eight hundred pulses applied to the input lead 269. The last stage 261 divides the frequency at the lead 21| by two so that one pulse is produced at the lead 249 for every 1600 pulses applied to the lead 269 and the k. c. output of the generator 241 is reduced to 62.5 cycles per second.

This 62.5 cycle frequency is applied through va capacitor 212 and a lead 213 to the phase detector 250.

The variable frequency generator 252 includes an oscillator triode 20020|202 which is interconnected with a reactance tube 203 in a conventional manner to deliver at an output terminal 204 oscillations of a frequency dependent on (1) the reactance of the tube 293, (2) the selected tuning coil connected to the anode 200, and (3) the number of inductance units connected in series with this selected coil.

The output frequency of the generator is established at the desired reference frequency by means of a potential applied through a lead 205 to the grid 266 of a cathode follower 2116-201- 209 which is provided with a cathode load resistor 269. As is well known, the reactance across the oscillator tank circuit is thus established at a value dependent on the potential applied from the resistor 299 to the grids 2| 0--2|| of the reactance tube. This reactance is connected to the oscillator tank circuit in parallel with the selected tuning coil so that, if it is adjusted to a fixed value, the variation in the generator output frequency is produced by change in the tuning coil Vand in the inductance connected to a -l-B lead 246 in series with it.

The various oscillator coils beginning with the lowest frequency coil are indicated by the reference numerals 2|3 to 222. Connected in parallel with these oscillator coils are capacitors 223 to 232 respectively. The Various inductance units are indicated by the reference numerals 233 to 24|.

Selection of the various oscillator coils and inductance units is effected by four switches 242, 243, 244 and 245. Switch 243 selectively connects the oscillator coils to the grid 20| of the triode 260--20I-202. Switch 242 selectively connects the low voltage terminal of these coils to the anode 206 of the triode. Switch 244 selectively connects the high voltage terminal of the coils to a lead 246 of the inductance unit 24|. Switch 245 selectively connects the inductance units 233 to 24| to the +B terminal 2|2.

It will be noted that switches 242 and 244 are each provided with 11 fixed contact numbered from to Contacts to i0 are used to connect the various tank coils into the circuit, while contacts which are connected together, short the unused coils through the shorting rings. This is a customary procedure to eliminate undesirable effects from the unused coils. To obtain a frequency of 1195 k. c. switches 242, 243, and 244 would be on contact I0 and switch 245 would also be on contact I0. y

To reduce this output frequency by 5 k. c. steps.

QMQQMQQ v the. movable. contact or the.- switclr 245..' isv AInoved to engage the fixed contacts; 9; to. l successively until the. output frequency is reduced to 11-50. When the movable contacts or the switches 242. 243 and 244 are moved to theirnumber 9: positions and the movable contact of switch 245 is. moved to the number 10 position the +B. lead 2I2 is connected directly to the high voltage terminal. of thev 1145 k. c. oscillator coil 222 and this. coil is connected through the switchesv 242v and. 243. respectively to the anode 29.0 and the grid 29|. This output frequency of 1145 k. c. is reduced by 5Y k. c. steps by operation of. the; switch 245. as explained in connection with the 1195 k. c. oscillatorcoil 222. The same procedureA isrepeated. with each of the. oscillator coils 228,: to 2|3. The switches 242, 2.43 and 244, may be ganged together for simultaneous operation.

Itwill beA noted that the lead 295v is--connected .through a capacitor bank 21.4 to the output of' the phase detector 258.

Output pulses of a frequency from 7.00 k. c. to -1'195 k.. c. are applied through the lead284- to a frequency divider which includes stagesv 215 to 218. Thus such pulses areapplied through a ca pacitor 219, a coupling tube 280.- anct a. leadz 28| to the common anode terminal ofthe stage 215. Pulses of one half the input frequency are de livered from the right. anode ofthe stage 2115 through a capacitor 282', a lead 283, a coupling tube 284 and a lead 2185 tothe. common `anode terminal of the stage 216. Pulses or one fourth the input frequency are delivered from the right anode of the stage 216 through a capacitor 286, a lead 281, thel coupling tube 284 and a. lead 288 to the common anode terminal of the stage 2,11..

.Pulses of one-eighth theinput frequency are delivered from the right. hand anode of? the stage- 21-1. through a capacitor 28,9 to the common anode terminal of the stage 218. Pulses of onesixteenth -of the input frequency arev applied from thei right .hand anode of the stage 218 to the lead 255i.,

As indicated by Fig. 3, the lead 2,55; is connected to the adjustable cycle counter 254. through a capacitor 292 and a duotriode 293 which is so connected as'to differentiate theV pulses; 294 ofthelead 255 for applying to the adjustable cycle counter 254 pulses of the form indicated. by the reference numeral 295. The adjustable cycle counter of Fig. 3 includes la high speed decade comprising the ductriodeslll to 23, an intermediate speed decada comprising the duotriodes 24 to 21, a low speed decade comprising the duotriodes 28 to 3l and two additional duotriodes 32 and 33. Input pulses 295 of negative polarity are applied from a lead v34 through the crystal diodes 35 and 35 to the grids of the duotriode 28. Output pulses are. applied from an output lead 31 through a capacitor v38 to a reset circuit which` includes a duotriode 39 and a tetrode 49. The number ofl input pulses required to produce one output pulse is determined vby the 'setting of the vselector switches of the different decades. If the output frequency is to be main 'tained constant, it is necessary that. the setting of the selector switches be changed at yeachchang'e in output frequency.

These selector switches 81, 94, 95 and 95 which are shown immediately below the decades 'which they control, have their movable contacts con. nected through gates of the duotriode type. to the output terminal 31. Thus the three movable contacts 4I, 42 and 43 of the selector switchoi the decade 2li-23am..,connected throughthe ductriodea. 44:. 553ml 4B and.` the leads 41am! 4.8... tothe. .outputlead 31l so that .the lead 31 Eis made. more positive. when the count ofthe decade 21h-23 corresponds. to theA setting of the movable contacts. 4;|-.42w4i3; of the selector switch of this decade. Likewise the three movable contacts .49, 58` and 5l.; are. connected through aV duotriode 5.2- and a. lead 53 to the output lead 31 so that this. lead is made morel positive when the.' count of the decade 24e-2,1; correspondsy to the setting of the oontacts:49,.50and 5|. Similarly the three movable. contacts 54. I55. and 56 of the selector switch of the decade 28-3I and the single. mov; able contact 51 of the selector switch of the counter units 32 and 33 are connected through a duotriode 58, a lead 59 and the lead 48 to the output lead 31 so that this lead is made more positive when the count corresponds to the setting of the contacts 54 to 51. l

During'` the counting operation, the more pos.-` itive` potentials mentioned above mustv be simule taneously applied to the output lead 31 in order to. activate :the reset circuit. Thus' av morc'posis' itive. potential is: established at the lead 59- when;

the count to decade 28-31' and stages 32 and 33 corresponds to the setting of the contacts 54 to 51, at the lead 53 each time the count of decade 24;-2'1 corresponds to the setting of contacts 49, 58 and 5I, and at the 1ead 41 each time the count of the decade 29-23 corresponds to the setting ofthe contacts 4I, 42 and 43. When these three potentials are al1 at their most positive value, the reset tube 39 is biased on and one output pulse is. produced at a lead 601which is connected to a counter reset lead 6l and the output lead 82.

The character of the pulses produced at the leads 31 and 5 9 are to be discussed hereinafter in considerable detail for rthe reason that they relate to important features of the invention. As already indicated, these pulses are dependent on the potentials produced at` the fixed terminals of the various selector switches by the trigger cirv cuits of; which the counter isv constructed. It is therefore necessary to consider the circuit connections of the trigger circuits, their interconnections with one another, their connections to the fixed contacts of the. selector switches, and the arrangement of these xed contacts with ref spect toone another. t All the trigger circuits of the counter are ofa type wherein twotriodes each has its anode crossconnected to the grid of the other through a re`- sistor shunted by a capacitor so that current conduction is. in either one or the other of the triodes.

Thus the first trigger circuit of the decade 2,9423 hasits anode Heroes-connected to its grid 88 andj its anode 56 cross-connected to its grid 6.1.1 .The cathode of this trigger circuit is grounded through. resistors 63, and 54' and operati ing` potential. 11S-.applied to the anodes 55 and 5,8 troni. a reB. lead GQLthi'tough a resistor 18 which functions to maintain. aujtne ancees of niedecade.

at .the potential level'required for properv opera# tion of the counter with these connections, the 'applicationfbf a negative pulse from the lead 34 througnthediodc crystals35 and. 36. to the gridsl A81 and.Y 68. functions, in a well'lrnown manner to' transfer currentconduction from the conducting tothe non-conducting vtriode of the trigger cir.-vv cuit.

The other three., trigger circuits of the decade .2Q-23am similar to the -iirst. -vAll ofthern are connected tandem tlirxiuell.V the.. .coupling 7 capacitors 13, 14 and 15. An important feature Aof the decade 28-23 is the connection of the anode of tube 16 of the last stage through a crystal diode 11 to the right hand grid 18 of the third stage and through a diode crystal 19 to the right hand grid 80 of thesecond stage. With these connections, the operation of the decade 20-23 is as indicated by the following tabulation wherein the number of pulses applied to the input lead 34 are shown in the rst column and the current conducting condition of the various stages are indicated by R (right-hand triode) an L (left-hand triode).

Tabulation No. 1

It is apparent from the above tabulation that a negative pulse is produced at the anode of tube 16 of the last stage in response to right input pulses and at the anode 8| of this stage in re sponse to ten input pulses. l

Such negative pulse at the anode of tubeV 16 functions to transfer current conduction from the right-hand triodes to the left-hand triodes of the second and third stages so that the operating cycle of the decade 20-23 is completed in response to ten input pulses. This type of feed-back is disclosed in a copending application of I. E. Grosdoi, Ser. No. 580,446, filed March 1, 1945. Output pulses of negative polarity are fed to the input terminal 82 of the decade 24-21 through a capacitor 83 from one or the other` of the anodes 16 and 8| depending on the setting of the movable contact 83 which cooperates with fixed contacts 0, 2 and 3 (connected to the anode of tube 16)z and fixed contacts 4 to 9 (connected to the anode 8|). This switch as a whole is indicated by the reference numeral 84. Its purpose is hereinafter explained in connection with the form of pulse which is effective to operate the reset circuit previously mentioned.

' Associated with the decade 20-23 is a switch 85 which includes a movable contact 86 and fixed contacts to 9. The function of this switch is to connect the right-hand grid 68 of the rst stage to the reset lead 6| only when the stage is not in its zero count condition. The purpose of this is to avoid interference betweenthe input pulses which may be applied continuously andthe reset pulse which might otherwise operate thei stage to produce inaccuracy of the count.

The three point switch which controls 'the ap-'I` plication of the anode potentials of the decade 2li-23 to the gates 44, 45 and 46 is indicated by a general reference numeral 81 'for convenience of reference. It includes the movablelcontacts 4| 42 and 43 and three corresponding groups of xed contacts. Each group of iixed vcontacts is nurnbered i) to 8 like the fixed contacts of the switches 84 and 85. As indicated by broken lines, the movable contacts of the switches 84, 85 and 81 may be all-ganged together s'o that each 'movable contact engages the same numbered xed contact in all the switch positions.

By assuming any desired position of the switches 84, and 81 and referring to the above Tabulation No. 1, it is easy to see that the movable contacts 4|, 42 and 43 of the switch 81 are all least positive only when the number of input pulses corresponds to the particular switch setting. Thus if the switch 81 is set at the number 5 contacts which are connected respectively to the left anode of the first stage, the right anode of the second stage, and the left anode of the third stage, it is evident from the tabulation that the movable contacts 4|, 42 and 43 are all at their more negative potentials only when five input pulses have been applied to the lead 34. The same is true for all the other settings of the switch 81. As hereinafter explained in greater detail, these more negative pulses of the movable contacts 4|, 42 and 43 are combined and reversed by the triodes 44 and 45, then passed through the gate 46 to give a single reversed pulse, which is again reversed and amplified by the second half of .the duotriode 46 so that a more positive pulse is applied to the lead 41.

The remaining stages of the counter differ from the stages of decade 20-23 in that (l) anode potential is applied from the lead 69 through a common resistor 88 to the individual anode resistors, (2) input pulses are applied between the different stages through capacitors 83 to a terminal at the junction of the common and individual resistors, (3) the feed-back connections of the decades 24-21 and 28-3| are made through capacitors 90 to 93 instead of crystal diodes and (4) the feed-back in each decade is from the last to the third and from the third to the second instead of from the last to the second and third stages.

The use of crystal diodes in the grid circuits of the rst decade 20 to 23 has the advantage that it facilitates more rapid operation of this stage. The second and third decades operate at speeds which permit the use of capacitors through the circuit. It is, of course, apparent that the decade 24-21 counts tens, the decade 28-3l counts hundreds and the stages 32 and 33 count thousands. The operation of the decade 24-21 is apparent from the following tabulation wherein the input pulses are each indicated as a group of 10. 'I

Tabulation No. 2

wrrnd :cnr-@Hmm acariens mmm-1 were' est naamw ."The operation of the decade 283| is similar to that of the decade 24-21 with the exception that each impulse applied to it represents |00 pulses applied to the lead 34. Similarly each in- .put pulse to the stages 32 and 33 represents 1000 input pulses applied to the lead 34.

Three `'point yswitches 94 and 95 similar to the 4three Vpoint switch 81 are 'provided for applying the anode potentials of the decade 24-21 and the decade 28-34 respectively 'to the gate 52 and the -gate 58. Ganged with the switch 95, as indicated by a broken line, is a switch 90 by Wh'ch the counts of the stages 32 and 33 are combined with the counts of the decade 28-3I -to produce a result to be explained in greaterdetail.

rAssui'ning the switch "94 to be set for a count of 10, as indicated by the numeral 1 adjacent its corresponding iixed contact, it is "seen that the movable contact 49 is connected to the right-hand 'anode of the stage 24, the movable contact 50 connected to the left-hand anode 'of the stage 25, and the movable contact '!v is connected to the right-hand anode of the stage 21. Referring to Tabulation No.2, it is seen that all the anodes to which these movable contacts are connected are not conducting current in response to the 70th input pulse and are therefore at their more positive potentials. These more positive lpotentials are combined and amplified in the gate 52 and function to produce a more positive pulse at the lead 53. In the same manner, each setting of the switch results in a more positive potential at the lead 53 when the number of in? put pulses correspond to the selected setting of the switch 94.

While the decade 28--3l is similar to the decade 24-21, its three point switch 95 has somewhat diiierent arrangement of its xed contacts as indicated by the reference numerals which 'are adjacent the fixed contacts 'and have the same significance as in the cases of the switches 81 and 94.

Assuming the switches 95 and 96 to be .set in their illustrated positions, it will be noted that the contact v54 is connected to the left-hand anode `'of the-stage 28, the contact 55 is connected to the righthand anode ofthe stage 30, and the `Contact 56 is connected to the left-hand anode of the stage 3l. rSince all these anodes are not conducting current at a count of four hundred input pulses and are therefore at their more positive potentials, a more positive potential tends .to be applied to the gate 58. This potential is not suffi-cient to open 'the gate because of the negative potential applied to it from the righthand anode of the stage '32. When the num'- ber of input pulses reaches 1400, however, the gate 58 is opened and the lead 59 is made more positive.

As the movable contacts 54, 55, 56 and 51 are moved to the right, the gate 58 is opened successively in response to input pulses numbering 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200 and 2300. This particular arrangement is provided to facilitate the maintenance of a constant frequency of 31.25 cycles at fthe output terminal 62 While the input frequency at the lead 34 :is changed by equal steps from 43,750 to 74,687.5 cycles.

With vthe switch settings previously assumed, one output pulse is produced in `response to v1475 input pulses. `Such a single output pulse may be produced by input pulses numberedfrom 1400 to 2399 with the switches y95 and 96 ganged together as illustrated. Thus if the input irequency is 43,750 cycles and the output frequency is to be kept at 31.25 cycles, the selector switches are set at 1400. Similarly the selector switches are set at 1410 lfor an input frequency `of 16 cyc es at .i420 for an input frequency of at 1430 Afor an v'input frequency of .1,5 at 1440 for .an input frequency of at 1450 for an input` `frequency of etc.

As indicated fabov'e but not explained in detail, the anode voltages -of Vthe :various stages of the counter are applied through the three point selector Vswitches 01, l94 and 95 `and the one point switch 96 to 'the isolating tubes 44 and 45 and tothe 4gate tubes A46 52 -'and 58 for producing a reset or output pulse in response to a number of input pulses corresponding to the setting of the selector switches.-

These tubes 'are illustrated as of the duotriode type, only one of the triodes being utilized in the case of 44. The more negative `potentials of the switch 81 'are applied respectively to the grid of the tube 44 and tothe grids vof the tube 45. As a result, the tubes 44 and '45 draw less 'current through their anode resistors and a more posi`y tive potential fis applied to th'e left-hand grid of the gate 46. When all three `of the triodes of 46 and :'41 .are conducting, rsuf'cient voltage is applied to "the grid ftoloverride the bias and cause 46 to conduct, `'thus.ii'icrfeasing the current of its leftehand triode=and applying a more negative potential toits right-hand grid so that the current `'of `its right-hand Atrio'de vis reduced and a more positive potential is appliedto the lead 41.

In previously known means of combining the anode voltages of aidecade counter, it has been customary to -insert large visolating resistors in the fixed rcontact leads lofthe selector switch and to connect theaselected ones of these resistors through the movable #switch ycontacts to a common terminal vwhich is connected to the grid of the gate tube. The 'disadvantage of such a combining system is 4that the large isolating resistors in series with the input capacity of the gate tube produces a slope on the leading edge ofthe pulse applied to the gri-d Iof the gate tube so that the gate tube is operated a `fraction of a cycle late.

By using the three isolating triodes 44 and 45 as explained above, the .gate tube control'voltage wave is made to have about the same steepness as those of Athe anode voltage'waves. Atthe saine time there is 'maintained such complete isolation between .the `anode'sfof 'the decade as is required to prevent interference with the operation 'of the decade by variation in the selector switch settings.

It should 7be 'noted that vthe cathodes of the isolating tubes 44 land 45 Iare all connected together and are so biased as to vconduct only when a more' 4positive Vvoltage is applied from the selected anodes of the decade.

The operation iof the-fgate tubes 52 and 58 is readily understood without detailed explanation. When a ymore fpositive pulse is-applied from the selected .-ancdes to their left-#hand lgrids, more cycles cycles cycles cycles 11 current is drawn by their left-hand triodes, the potentials of their right-hand grids is made more negative, the current of their rightv hand triodes is reduced and more positive potentials are applied to the leads 53 and 59.

The more positive potential which is applied to the lead 31 in response to the selected number of pulses applied to the input lead 34 is now to be considered in connectionwith Figs. 4 to '1. Fig. 4 is a diagrammatic indication of the composition of the potential applied to thef lead 31. The potentials applied through gate 46 are indicated by straight lines, the potentials applied through the gate 52 are represented by square waves of short width, and the potentials applied through the gate 58 are indicated as square waves of larger width. Y X

It will be noted that these gated potentials are super-imposed on one another, as indicated by the reference numeral 91, when the number of pulses applied to the input lead 34 corresponds to the setting of the selector switches 81, 94, 95 and 96. This pulse 91 makes the right-hand grid .of the peak detector 39 more positive, more cur- As a result, the tube triggers, drawing a large pulse of current through its cathode resistor and a positive pulse potential is applied to the lead 60. This potential is applied (l) to the output lead 62 and (2) to the reset lead 6l which is connected to the right-hand grids of the various stages of the counter. VWhen this more positive potential is so applied to these righthand grids, al1 the stages of the counter are reset to their zero count or standing condition with current in their right-hand anodes. The effect of this on the potentials at 31 is shown in Fig. 5.

In connection with Fig. 4, it has been assumed that all the voltages change instantaneously. Actually, the step from the potential of the second gate to that of the first gate may' have a curvature on its front edge as indicated at 98 in Figs. 6 and 7 wherein the anode potentials of the first and second decade are shown much wider than in Fig. 1. Assuming the pulses of the rst gate to have straight sides, this curvature results in a control and reset pulse occurring a fraction of a second later than it should.

Such inaccuracy is minimized or obviated by the provision of the switch 84 connected' between the flrst and second decade. This switch functions to advance the time (but not the rate) at which pulses are fed to the second decade when its movable contact 83 is in engagement with the xed contacts 0 to 3. The resulting effect, as indicated by Fig. 7, is to advance the beginning of the second gate potential so that the rst gate potential is not superimposed on the curved portion 98 of the second gate potential. In this' manner, correct timing of the reset and output pulses is assured. This featureis of course useful in many other cases where superimposed voltages are derived through a plurality of gates from sources of potentials which are of a wave form subject to curvature.'

In resettinga variable frequency counter, such as that of the present invention, the most critical point is the first stage of the high frequency decade. For all odd numbered settings of the selector switch, this rst stage must be reset and ready to operate in kless than Vone vcycle so that Sil no counts are missed. For all even numbered settings of the selector switch, the first stage must not be reset and must not hold over for an extra cycle. These conflicting requirements are met by applying the reset potential to the right-hand grid of the rst stage of the high frequency deo ade only on the odd counts. This is accomplished by the switch which has its odd numbered fixed contacts connected to the reset lead 6| and has its movable contact 86 connected through a relatively high resistance to the right-hand grid of the first stage so that the reset pulse applied to this grid is of an amplitude reduced to the optimum value for the condition under which this stage is operated.

The substantially constant frequency of about 31.25 cycles per second is fed from the adjustable cycle counter 254 through the output lead 62 to the phase detector 250, the circuit connections of which are shown in Fig. 2. This phase detector includes four diodes 296-291, 298-299, 390-301 and 302-303. Potential of a wave form indicated at 304 and a frequency of 62.5 cycles per second is applied through the lead 213 to the leads 305 and 306. It will be noted that the lead 305 is connected to the cathode 291 and to the anode 300, that the lead 396 is connected through resistors 301 and 308 to the lead 62 through which the 31.25 cycle pulses are applied from the adjustable cycle counter 254, and that the lead 62 is connected through a resistor 309 to the primary circuit of a transformer 3I0. The secondary circuit of this transformer is connected to the anodes 296 and 298 and to the cathodes 36| and 303 through a resistor 3H which is shunted by a capacitor 3I2. The cathode 291 and anode 300 are connected to ground through a resistor 313 which is shunted by a capacitor 3 I4 and the cathode 299 and anode 302 are connected to ground through the capacitor bank 214 from which potential is applied to the grid of the cathode follower `206-201-208 for regulating the reactance of the tube 203.

Assuming that various circuit components of f the phase detector to have the values indicated by the legends placed adjacent to them, the potential applied to the grid 206 of the cathode follower is determined in a well known manner by the phase relation between the 62.5 cycle and 31.25 cycle pulses applied to it respectively through the leads 249 and 62. Thus if the fre-1 quency of the pulses at the lead 62 tends to in-A crease, a more positive potential is applied to the grid 206 so that the potential across the resistor 209 is increased, the reactance of the tube 203 is decreased and the frequency of the variable frequency generator is reduced. When the frequency of the pulses at the lead 6'2 tends to decrease, the opposite eiect is produced. Thus the variable frequency generator delivers at its various selected frequencies an output frequency which is maintained with crystal controlled ac-I frequency generator, a frequency divider connect-y ed between said constant frequency generator and said phase responsive device, means including a frequency divider of adjustable division ratio con-v;

nected between said controllable frequency generator and said phase responsive device, and means interconnecting said phase responsive device and said controllable frequency generator for regulating the output frequency of said controllable frequency generator in response to vchange in the phase relation between the output lpulses of said generators.

2. The combination of a constant frequency source, a controllable frequency generator, an adjustable division ratio frequency divider connected to the output of said generator, means for simultaneously controlling the frequency of said generator and the division ratio of said divider so that the output frequency of said divider is maintained at a substantially constant value, and means responsive to the phase relation between the outputs of said source and said divider for stabilizing the frequency of said generator.

3. The combination of a controllable frequency generator, an adjustable division ratio frequency divider connected to the output of said generator, and unitary means for changing said frequency and said division ratio so that the output frequency of said divider is maintained substantially constant.

4. The combination of a controllable frequency generator, an adjustable division ratio frequency divider` connected to the output of said generator, and unitary means for changing said frequency and said division ratio so that the output frequency of said divider is maintained substantially constant and means responsive to each output pulse of said divider for resetting said divider to its standby condition.

5. The combination of a constant frequency source, a controllable frequency generator, an adjustable division ratio frequency divider connected to the output of said generator, means for simultaneously controlling the frequency of said generator and the division ratio of said divider so that the output frequency of said divider is maintained at a substantially constant value, a phase detector connected to said source and to the output of said divider, and means including a 14 cathode follower connected between said detector and said generator, for stabilizing the output frequency of said generator.

6. The combination of a constant frequency source, a controllable frequency generator, an adjustable division ratio frequency divider connected to the output of said generator, means for simultaneously controlling the frequency of said generator and the division ratio of said divider so that the output frequency of said divider is maintained at a substantially constant value, phase responsive means connected to said source and to the output of said divider, a reactance tube connected to said generator, and a cathode follower connected between said phase responsive means and said reactance tube for stabilizing the frequency of said generator.

'7. The combination of a constant frequency source, a controllable frequency generator, means for changing the frequency of said generator by discrete steps, a frequency divider responsive to the output frequency of said generator, means for controlling the division ratio of said divider in accordance with said steps and maintaining the output frequency of said divider at a substantially constant value, and phase responsive means responsive to the outputs of said source and said divider for stabilizing the output frequency of said generator at each of said steps.

8. The combination of a constant frequency source, a controllable frequency generator, means for changing the frequency of said generator by discrete steps, a frequency divider responsive to the output frequency of said generator, means for controlling the division ratio of said divider in accordance with said steps and maintaining the output frequency of said divider at a substantially constant value, and means responsive to the outputs of said source and said divider for stabilizing the output frequency of said generator at each of said steps.

JOHN D. WOODWARD.

N o references cited. 

